1. Field of the Invention
The present invention relates to the shape of a magnetic head slider which is suitable for a magnetic disk having a smooth surface and has the extremely low flying height of 20 nm or less, particularly relates to a head slider used in a state in which the head slider is normally or intermittently in contact with a magnetic disk and particularly relates to a magnetic head slider the friction force and vibration in contact of which are reduced and a magnetic head slider assembly using it.
2. Description of the Related Art
The recording density of a magnetic disk apparatus is remarkably increasing and recently, a magnetic disk apparatus having the recording density of 10 Gbits or more per 1 in2 is published. To achieve such high recording density, it is essential to put a magnetic head close to a magnetic recording layer of a magnetic disk and currently, an interval between them is 20 nm or less.
In a recent magnetic disk apparatus, to narrow the interval possibly, the surface roughness of a magnetic disk is required to be reduced possibly. As a result, in place of a conventional type contact start-stop system that when the rotation of the magnetic disk is stopped, a magnetic head comes in contact with the magnetic disk and when the magnetic disk starts to be rotated, the magnetic head floats by its airflow, a loading-unloading system that when the magnetic disk is stopped, the magnetic head retreats (is unloaded) from over the magnetic disk and when the magnetic disk starts to be rotated, the magnetic head is loaded over the magnetic disk is being adopted. In this case, the wear resistance is slightly enhanced, however, the magnetic disk is required to bear with mechanical shock in loading and the contact of the magnetic head due to the abnormality of the posture which may suddenly occur even in normal operation. As currently flying height is remarkably small, large friction force is made and a head slider largely vibrates when the magnetic disk having a smooth surface and the head slider come in contact and read/write may be disabled.
A magnetic disk is formed by sequentially laminating an underlayer, a magnetic layer, a protective layer and a lubricant layer on a non-magnetic substrate such as an aluminum alloy substrate and a glass substrate. For the surface roughness of the current magnetic disk, it is general that averaged center line roughness Ra on a data surface is approximately 0.5 to 2.5 nm. For the material of a lubricant layer, it is general that liquid lubricant made of perfluoropolyether is used and it is general that the thickness is 1.0 to 3.0 nm.
A burnishing head is used in a process for removing a projection called a burnishing process or a process for cleaning in a final process for manufacturing a magnetic disk as disclosed in Japanese published unexamined patent application No. Hei10-112023. In the patent application, technique for avoiding adhesion by roughing the surface roughness of the burnishing head because the burnishing head adheres to the magnetic disk and the effect of removing a projection and dirt cannot be fulfilled in case the surface roughness of the magnetic disk is small is disclosed.
A glide head is used in a projection detecting inspection process for attaching a piezoelectric element to the back of a head slider and detecting that the projection of a magnetic disk comes in contact as disclosed in Japanese published unexamined patent application No. Hei11-37748. The flying height of the glide head is currently 10 nm or less and when the glide head comes in contact with the magnetic disk, large friction force is made and the glide head may scratch or strike the magnetic disk.
A head for an error check is a head for checking a detect of a read/write signal from/onto a magnetic disk as disclosed in Japanese published unexamined patent application No. 2000-55883 and a read/write element is mounted in the vicinity of the air trailing edge of a head slider. A process for assembling a magnetic disk apparatus includes a servo track recording process which is a process for writing a servo signal onto the magnetic disk and a head called a clock head for writing a reference signal onto the magnetic disk is used at that time. The clock head often writes a clock signal in the vicinity of the outer edge of the magnetic disk, in the process, the head and the disk come in contact and in case the magnetic disk is flat, normal recording may be disabled or the disk may be damaged.
In the contact start-stop system, the smaller the surface roughness of a magnetic disk is and the flatter the surface of the magnetic disk is, the more stiction becomes and the stiction hinders the starting of a magnetic disk apparatus. Then, in Japanese published unexamined patent application No. Hei6-203514, technique for reducing stiction by providing a stepped projection to the surface of an air bearing of a slider is disclosed. This well-known patent application shows that area in which a magnetic disk and the slider are in contact is reduced by setting the height of the stepped projection so that the value is larger than 0.01 μm and is smaller than 1.5 μm and the stability of the flying slider and the reduction of stiction are enabled by reducing the contact area. However, in the patent application, it is not disclosed whether there is the effect of reducing friction in case the head comes in contact with the magnetic disk at high speed or not.
In Japanese published unexamined patent application No. Hei11-25629, a head slider provided with the similar stepped projection to that in the well-known patent application the slope angle of the surface of an air bearing of which with a recording surface of a magnetic disk, that is, the pitch angle of which is 0.5 to 1.5 mrad is disclosed. In this well-known patent application, the contact area of the head slider and a magnetic disk is reduced by using the magnetic disk the averaged center line roughness Ra of which is 1 nm or less and adjusting the height of the stepped projection so that the pitch angle has the value described above and as a result, stiction is reduced. In the well-known patent application, technique for reducing friction in contact at high speed is also not disclosed.
In Japanese published unexamined patent application No. Hei9-245451, technique for reducing the contact area of a magnetic disk and a head slider in a state in which a projection is formed on the surface of an air bearing of the slider and the magnetic disk is static and avoiding adhesion as a result is disclosed. In this well-known patent application, it is shown that the smaller the surface roughness of the magnetic disk is, the smaller the area of the projection on the surface of the slider is required to be. In Japanese published unexamined patent application No. Hei8-102164, technique for reducing the contact area of a slider and a magnetic disk by forming difference-in-stage made of a thin film in a part of the surface of the slider and reducing static friction is similarly disclosed. However, technique for reducing friction in contact at high speed is also not disclosed in these well-known patent applications.
In Japanese published unexamined patent applications No. Hei10-49850 and No. Hei11-185418, for a method of reducing difference between flying height in the position of a read/write element and flying height at an air trailing edge in a slider provided with difference-in-stage in the vicinity of an air leading edge of the slider, a method of controlling an angle between the surface of an air bearing and the surface of a magnetic disk and reducing distance from the element to the lowest point of the air trailing edge by tapering a part at the air trailing edge is disclosed. For a well-known patent application related to a suspension of a slider, there is also Japanese published unexamined patent application No. Hei6-119736. This well-known patent application discloses a suspension provided with two movable parts of the side of a base plate for fixing the suspension and a part bonded to the slider to reduce the out-of-plane stiffness of a head and reduce the dispersion of a load onto the slider. However, in these patent applications, technique for reducing friction in contact at high speed is also not disclosed.